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In this work we use analytical and 3D numerical modeling tools to analyze data from InP/In0.53Ga0.47/InP double layer planar 15 pixel pitch focal plane arrays (FPAs) designed to image in the near infrared to determine array suitability for operation under low-level illumination, including overcast, “Night Glow”- only conditions. Notable is that the diffusion dark current component is the dominant current component near and above 300K and is limited by band-to-band radiative recombination processes. The Shockley- Read- Hall (SRH) minority carrier lifetime is τSRH =107μs. Recombination through band gap states in the space charge region (SCR) situated at the intrinsic Fermi level is the dominant component for temperatures below 300K as previously demonstrated using 3-D numerical simulations consisting of both bulk area and perimeter dependent components. 3-D numerical simulations in combination with scanning capacitance microscopy are paramount to characterizing the Zn-diffused p+n shallow step homojunction and to identifying technology limitations in small pitch high density (FPAs). Photon recycling effects, i.e., effects caused by repeated trapping of photons, are not observed in the measurements of the minority carrier lifetime and the diffusion dark current component. As a result, the diffusion current component Jdiffusion α to the radiative recombination rate Gr(α) and the radiative minority carrier lifetime τradiative = 1/BNd, where B is the radiative recombination coefficient and Nd the majority carrier concentration.

This paper correlates measurements of minority carrier lifetime using photoconductivity transient or photoconductive decay (PCD) with measurements and analysis of current–voltage (I–V) on P + n photodiodes of the same layer. This analysis is done at the primary temperature of operation near 77 K. Measurements of minority carrier lifetime in n-type molecular beam epitaxy Hg1−x Cd x Te (MCT) on variable substrates of GaAs and CdZnTe are presented. The minority carrier lifetime from I–V analysis of P + n long-wave infrared (LWIR) photodiodes on CdZnTe (CZT) and GaAs substrates is similar to PCD analysis. Deviations occur for MCT/GaAs in the low-temperature extrinsic region associated with Shockley–Read–Hall (SRH) at 78 K in contrast to MCT/CZT at similar temperatures. The x-values in the formula Hg1−x Cd x Te for samples grown on CdZnTe and GaAs are 0.22 and 0.235, respectively. I–V analysis of variable-area LWIR photodiodes shows a calculated minority carrier diffusion coefficient of 2.3 cm2/s on lattice-matched CZT and 3 cm2/s on non-lattice-matched GaAs with diffusion lengths of approximately 24 μm and 20 μm, respectively.

Mid wave infrared (MWIR) imaging in the 3-5 um spectral band has traditionally been performed by InSb sensors. InSb technology is presently limited to a near 80K operating temperature and the hunt has been on for a higher operating temperature (HOT) technology that does as well at 150K as InSb at 80K, but with reduced power requirements. Amongst these alternative technologies are photovoltaic sensors consisting of heterostructures of HgCdTe (MCT). In previous work we assessed the device performance of several alternative MWIR HOT technologies (MCT on Si, MCT on GaAs) as a function of operating temperature. In this work we compare the NEDT histograms for these alternative technologies with InSb to better understand how their performance can be improved at higher temperatures. We also present analysis formalism for quantitatively assessing the number of FPA pixels which reside in the central versus the shoulder portions of the histogram.Begin the Introduction two lines below the Keywords. The manuscript should not have headers, footers, or page numbers. It should be in a onecolumn format. References are often noted in the text1 and cited at the end of the paper.

Well recognized are the potential benefits in camera simplicity, power reduction and increased cooler life associated with the capability of operating infrared focal plane arrays at or near room ambient temperatures. Quality imagery in the 3 to 5 mm spectral band at scene temperature of 300K with focal plane array temperatures up to 175K was demonstrated recently. The array consisted of 640*512, 16 mm pitch N+p(As) detector elements grown by metal organic vapor phase epitaxy on a GaAs substrate. In this paper, a carrier recombination model is presented that explains the dark current density data as a function of inverse temperature. Basically the dominant carrier recombination occurs through ionized donor-like flaws centered in the upper half of the energy gap. For Hg1-xCd x Te, x=0.3 and 0.2867 materials, the flaw energy level, Eflaw(0K) respectively, is centered at 0.189 eV and 0.1181 eV above the valence band edge; The shortest possible lifetime tp0 for hole capture respectively is 3.5 and 550 ms. Band to band recombination is not observed to be dominant even in the temperature region T a 300K, where the radiative and Auger lifetimes are significantly smaller than tp0. The asymmetry parameter g = tn0/tp0 ll1.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Reported is a detailed analysis of the dark current versus voltage versus temperature data of planar hetero-structure P + n mid wavelength infrared MWIR photodiodes with band gap energy E g (78K) = 0.243 eV, λ g = 5.1 μm and long wavelength infrared LWIR photodiodes with E g (78K) = 0.115 eV, λ g = 10.8 μm. The purpose of the investigations is to identify the dominant carrier recombination mechanisms and in particular to determine at what temperature and voltage is the onset of Shockley Read Hall (SRH) space charge currents. The important finding is that the currents can mostly be explained by a combination of Auger (e-e) and radiative carrier recombination processes with no evidence of SRH recombination through near mid-gap states; a lower bound estimate of the SRH lifetime for LWIR photodiode is 100 μs. Intrinsic radiative recombination is found to be the dominant carrier recombination mechanisms for the MWIR photodiode with a carrier concentration N d =10 15 cm -3 , and Auger (e-e) being dominant for the LWIR photodiode. The LWIR Auger (e-e) lifetime data is well fitted with the Beattie, Landsberg and Blakemore (BLB) formulas with a constant overlap integral F1F2= 0.15, which is in accord with recent electronic band structure calculations. From the analysis of variable area LWIR photodiodes the minority carrier conductivity mobility and diffusion length at 80K are calculated to be 350 cm 2 /V-s and 23 μm respectively. The LWIR lifetime measured by the photoconductive decay method is in agreement with the expected intrinsic Auger (e-e) lifetime ≈ 2 μs at 80K and with the lifetimes obtained from device analysis. For T ≤ 40K, trap assisted tunneling is the dominant current in reversed bias LWIR photodiodes; forward bias currents are dominated by diffusion currents of origin in the n- layer. For the MWIR photodiode deviation from diffusion limited behavior to G-R is observed at T < 80K and, the SRH lifetimes ιn0 and ιp0 are estimated to be 50 ms. Measured and calculated external quantum efficiencies at the peak responsivity wavelength λpk for both MWIR and LWIR photodiodes are ≈ 70% at 78K. For imaging in the 3-5 μm spectral band scene temperature 300K, F/3 optics, the noise equivalent temperature difference NEuT of MWIR photodiodes is calculated to be near background limited performance BLIP =12.4 mK for detector temperatures Td ≤ 150K.

In this work the current versus voltage data of a p-n+ junction is converted into minority carrier lifetime data. Space charge recombination currents dominate at modest reverse bias at 80K and taking the dominant recombination centers to be located at the intrinsic Fermi level, the lowest minority carrier lifetime τ0 is determined to be 35ns. This single Shockley-Read-Hall carrier recombination parameter provides an excellent fit to the data over temperature range 40K≤ T≤ 130K; the 35ns minority carrier lifetime also explains the quantum efficiency data. The transition from diffusion to space charge currents occurs for temperatures, T ≤ 100K. For T≤ 40K trap assisted tunneling is the dominant current component. Based on imaging system requirements to be near background limited for photon flux ≈ 1015 ph/cm2-s and detector temperature of 80K, the minority carrier lifetime will need to be increased by one order of magnitude.

Backside illumination of Hg 1-x Cd x Te photodiodes at low temperature increases the low frequency excess noise. The photodiodes tested were formed by ion implantation of LPE Hg 1-x Cd x Te on CdTe substrates. During illumination, the excess noise increase is proportional to the photocurrent for backgrounds which induce a current in the 10-5A cm-2range. After illumination the increased dark current and excess noise in a reverse biased diode persist for hours in some of the diodes tested. Persistence is not observed after illumination for zero bias.